Piston structure and combustion chamber



0, 1957 L. D. BURCH 2,803,237

PISTON STRUCTURE AND COMBUSTION CHAMBER Original Filed Dec. 17, 1953 3 Sheets-Sheet l INVENTQR ATTORNEY Aug. 20, 1957 D. BURCH PISTON STRUCTURE AND COMBUSTION CHAMBER 3 Sheets-Sheet 2 Original Filed Dec. 17, 1955 ATTORNEY Aug. 20, 1957 L. D. BURCH I PISTON STRUCTURE AND COMBUSTION CHAMBER Original Filed Dec. 17, 1953 s Sheets-Sheet s ATTQRNEY United States Patent-G M PISTON STRUCTURE AND COMBUSTION CHAMBER Lewis D. Burch, Dear-born, Mich.,.ass ignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware "Division of application Serial No. 398,758, December 17, 1953. This application January 26,1955, SerialNo. 484,189

16 Claims. .(Cl. 123-191) The present inventionrelates to engines and more particularly to spark ignited internal combustion engines. 'This is a division ,of application Serial No. 398,758 :by

Lewis D. Burch filed December 17, 1953.

In order to obtain the .maximum .efhciencyfrom an internal combustion engine, it is desirable .to utilize as .high a compression ratio as possible. However, when the gaseous charge in a cylinder is highly compressed, the temperature of the confined gases is greatly increased. In addition, during the initial burning of the explosive charge and the expansion thereof, the unburned end gases will be compressed thus further increasing the temperature :of the end gases. As the temperature ofthe remaining charge approaches the kindling point of the .gases, pre-ignition and detonation frequently occur. These phenomena not only decrease the efliciency but. are structurally detrimental to'the engine. .In .order ,to. reduce the tendency toward detonation and pre-ignition, it has beenthe practice to employ combustion chambers which include a compact firing zone and 'a quench zone having a relativelylarge surface-to-volume ratio. In combustion chambers of this design the large amount of surface area will cool the end gases sufficiently to keep the temperature below the kindling point and thus prevent detonation and/or-pre-ignition. In the past, these chambers have been more or less unsymmetrical with the flame front originating on one side of the chamber and traveling toward the other side. This frequently causes the flame front to reach one side of the ,cylinder before it reaches the other side. This nonsymmetrical burning produces unbalanced forces .on the face of the piston which tend to cause the axis of the piston to be misaligned with respect to the axis of the cylinder.

It is proposed to provide a combustion chamber which will produce a balanced resultant force on the face of the piston. This is to be accomplished by. providing a combustion chamberhaving aspark plug disposed in substantial alignment with the axis of the cylinder. .A compact firing zone isdisposed symmetrically about the spark plug While an annular quench zone is disposed symmetrically about the firing zone. This objective may be 'easily obtained by employing a combustion chamber which is defined by true surfaces of revolution disposed symmetrically about the axis of the cylinder. If the spark plug is positioned on this axis and the flame front travels at the same speed in all directions, the flame front will reach all portions of the periphery of the firing zone at substantially the same time. Also the flame front will reach all portions ofthe periphery of the annular quench zone simultaneously. Thus the flame front will always be symmetxrically disposed about the axis of the cylinder and accordingly, the forces on the face of the piston will be substantially balanced at all times. This symmetrical annular quench zone will also have the additional advantage that a large volume of end gases may be burned in thequench zone While still maintaining the advantages of a short flame travel in the quench ;zone. It isthus possible to ,obtain any esired proportion between the volumes of the quench axis of the cylinder.

Patented Aug. 20, 1957 zone and the firing zone without producingexcessively long flame travel.

It is alsoproposed to position the annular quench zone :so as to'provide a squish zone that willdirect a flow of turbulent gasesalong the walls of the combustionchamber. By employing a symmetrical annular squish zone, the gases will flow radially inwardly toward the electrodes of the spark plugat a substantiallyuniformrate in all portions of the combustion chamber. This flowwill not only provide a thorough scrubbing of the wallsand valves .but

it will also provide the maximum amount of turbulence 'possibleheretofore. Thus for-any given-sizeofcombustion; c hamber, it is now possible-to employ larger valves without interfering with'the engine operation.

It-should be noted that if the valves are disposed on the opposite sidesof the combustion chamber, it is possible to position the intake and exhaust valves adjacent the opposite sides of the cylinderhead. This in turn will permit the intake and exhaust; passages that interconnect the valve seats with the manifoldsto be as short, as possibleand also as straight as possible.

In order for the piston of areciprocating engine to move freely in the cylinder of the engine, it is necessary to have a certain amount of clearance between the piston, and the walls of the cylinder. 'Due to this clearance and the fact that the piston drives a rotating crankshaft by means of a reciprocating connecting rod, there is a'tendency for the axis of the piston to become misaligned with respect to the The forces produced by the movement of the piston and connecting rod and any unbalanced forces caused by the non-symmetrical burning of the gases in the combustion chamber will contribute to the axis misalignment of the piston. Movement of the piston into and out of alignment causes so-called piston slap. The slap not only causes objectionable noises but also produces excessive wear on certain portions of the cylinder Walls and the piston.

It is proposed to attach the connecting rod to'the piston so the forces applied to the piston will tend to produce a righting couple that will provide a more nearly balanced piston assembly. This is to be accomplished :by attaching the connecting rod to the piston by means of a wrist pin located between the piston rings and the face of the piston. This will tend, to place the center of the resultant forces on the piston either coincident with or even below the axis of the Wrist pin.

As an engine is placed in operation, the temperature of the piston will rise. This will cause the piston to expand so as to be considerably larger than when itris, cold. In order to allow for the thermal expansion that will occur as the piston becomes heated, the piston is made small enough so that as it becomes hot it will expand and fit the cylinder. In order to prevent piston slap when the piston is cold, the piston skirt is made elliptical with the major diameter normal to the axis of the wrist pin andsubstantially equal to the diameter of the cylinder. The piston is constructed so that the skirt will expand only along the minor diameter until the skirt becomes round and fits the cylinder at all points. However, since the head of the piston contains planar surfaces, ;it is necessary to make the head end of the piston circular because it must expand 3 uniformly in all directions. Thus when the piston is cold, the wrist pin will prevent piston slap in one direction and only the bottom of the skirt will prevent slapin the direction normal thereto.

It is proposed to utilize a piston having a surface of revolution on the end thereof. It will thus be possible to make the cross section of the piston elliptical over its entire length so that when it becomes hot, it will have a circular shape. This will allow the entire length of even a cold piston to engage the cylinder walls and reduce piston slap.

By employing a piston in which the wrist pin is disposed above the rings and the entire length of the skirt engages the cylinder wall, it will be possible to decrease the over-all length of the piston. Shortening the skirt in this manner in combination with the wrist pin being disposed above the piston rings will permit the use of a very short piston. This will not only decrease the weight of the piston but it will also permit the use of a much shorter cylinder which in turn allows a material decrease in the size of the engine without decreasing the piston stroke.

In V-type engines and particularly V-eight engines the intake manifolds employ a pair of main distribution passages that receive the combustible mixture discharged from the carburetor. Each end of a distribution passage communicates with a branch passage which has the opposite ends thereof adapted to discharge the combustible mixture into an intake port for one of the cylinders. In order to obtain the desired distribution of fuel charges into the various cylinders, the passages in the manifold are disposed in a criss-crossing relationship. This prevents any of the passages being disposed in a plane and necessitates that portions thereof be located one above the other. This results in a complex structure and in order to mass produce such a manifold it must of necessity be a heavy casting. Also due to the necessary disposition of the passages, it is extremely dilficult, if not impossible, for all of the passages to be of identical dimensions.

It is proposed to provide an intake manifold of the flat or planar type in which the various passages in the manifold may be disposed in the same general level without any of the passages crossing each other. This will permit a simple structure which may be either a light weight casting or inexpensively fabricated from sheet metal. This is to be accomplished by employing a plurality of distribution passages that extend outwardly from a. common distribution chamber so as to communicate with the centers of branch passages that have the opposite ends thereof in communication with the intake ports for the cylinders. The distribution passages which are disposed in side by side relationship and not in criss-cross relationship may be of substantially identical dimensions so as to insure uniform charges being delivered to all of the cylinders.

At the present time V-type engines are provided with a. separate head for each bank of cylinders and a separate intake manifold which in the case of valve-in-head engines is connected between the heads. Due to the necessity for employing heavy castings for the present intake manifolds, it is impractical to combine the heads and manifold. However, using the simplified intake manifolding described above will permit the heads and manifold to be combined into an integral structure. Among other ad vantages of this arrangement will be the elimination of the camshaft gallery cover and numerous gaskets, etc.

Since the heat rejection from the engine to the cooling water determines the size of the cooling system, it is desirable to provide cooling for the minimum number of parts in an engine. Accordingly, it is proposed to provide a head in which it is necessary to provide only a minimum amount of coolingfor the walls of the combustion chamber and the area around the intake and exhaust valve seats. By employing a head embodying the previously described combustion chamber with its large amount of quench area, the necessity for cooling of the walls of the combustion chamber is greatly decreased. By cooling the area around the valve seats, the valves will remain at satisfactory operating temperatures. Since no useful end is accomplished by cooling not exhaust gases that are to be expelled into the atmosphere, it is proposed to allow the minimum amount of heat transfer from the exhaust gases to the cooling water. This is accomplished by placing the exhaust valve seat adjacent the outboard edge of the head. Thus by placing the exhaust valve stem at the proper angle, it is possible to provide a straight exhaust passage from the valve seat to the exhaust port in the side of the head. Since the valve seat and exhaust port are as close together as possible and a straight passage is employed, the amount of travel of the hot exhaust gases through the head is a minimum distance. Thus the heat transfer to the head is reduced to a negligible amount and it is possible to eliminate useless cooling of the exhaust gases without a detrimental effect on the engine operating temperature. This will permit a material decrease in the volume of cooling Water and the size of the attendant cooling jacket and radiator. Also since the head embodies the above described turbulent combustion chamber, there will be a complete mixing of the liquid fuel particles in the combustible charge and, accordingly, it will not be necessary to rely on heating of the intake passages. This will eliminate the necessity of a cooling jacket about the intake passages thus permitting further reductions in the volume of cooling water.

These and other objects and advantages of the present invention will become more fully apparent as the description progresses.

Referring to the drawings:

Fig. l is a side elevational view of an engine employing the present invention.

Fig. 2 is a plan view taken substantially along the plane of line 22 of Fig. 1 showing an intake manifold for the engine.

Fig. 3 is a cross sectional view taken substantially along the plane of line 3-3 of Fig. 1.

Fig. 4 is a plan view taken substantially along the plane of line 44 of Fig. 8 and showing a piston for the engine.

Fig. 5 is a schematic representation of a crankshaft suitable for use in the present engine.

Fig. 6 is a cross sectional view of the piston taken substantially along the plane of line 6-6 of Fig. 8 and showing one form of a wrist pin.

Fig. 7 is an exploded perspective view of the wrist pin assembly of Fig. 6.

Fig. 8 is an enlarged view of the piston and valve assemblv of Fig. 3.

Referring to the drawings in more detail, the present invention may be embodied in any suitable engine 10. In the present instance the engine 10 is of the so-called V-type having two banks 12 and 14 of aligned cylinders l, 2, 3. 4, 5, 6, 7 and 8, the axes of which are downwardly convergent toward the bottom of the block 16. Each set of cylinders extends diagonally through the block 16 to form a series of circular openings 18 in the planar faces 20 and 22 formed along the upper edges of the block 16. Any suitable crankshaft 24 such as a four throw crankshaft may be mounted in the bottom of the block 16 in substantial alignment with each bank of cylinders. One end of the crankshaft 24 may be adapted for receiving a flywheel suitable for connection to a vehicle drive shaft. The opposite end of the crankshaft 24 may be provided with a pulley 26 suitable for driving the usual engine accessories such as a fan 28 and water pump 30. An oil pan 31 may be provided on the bottom of the block 16 to enclose the crankshaft 24 and form a sump for the engine lubricating oils.

A piston 32 of any suitable design may be provided in each of the cylinders for reciprocating movement therein. In the present instance each of these pistons 32 includes a.cylindrical:skirt.34. and a convex face 36 on theupper end thereof. Since there isa clearance-between the skirt 34. and the cylindenwalls 38 so as to permit free. reciprocating movement of the piston 32, sealing. means may be provided toprevent the passage of gases between the skirt 34 and the cylinder walls 38. This sealing. means may include a plurality of annular grooves 40 in the skirt 34. adapted to receive resilient piston rings 42 for sliding. engagement with the cylinder walls 38.

The convex face 36 on the upper end of the piston 32 forms onewallv of the combustion chamber 44, and accordingly, the shape of this surface will be determined by the designof the combustion chamber. In the present instance, this faceis a dome 46forming a convex surface of revolution, the detailsof which will be described in connection with the combustion chamber.

Each reciprocating piston 32 is drivingly coupled to a throwv 47; 48, 49M 50 on the crankshaft 24 by means of a suitable. connecting rod 51, 52, 53, 54, 55, 56, 57 or 58. The lower end of each of the connecting rods may beprovidedwith a bearing suitable. for attachment to one of the throws of the crankshaft 24. The'upper endv of each of the rods are provided with bearing means 59 for connecting it to the. insideof the piston 32. If the connecting rod isattached to the piston 32 above the resultant of theforces acting on the piston 32', there will be a righting couple that will tend to maintain the piston axis in substantial alignment with the cylinder axis. Therefore, in order to provide a more balanced piston assembly, the connecting rod is preferably attached to the piston 32 as close as possible to the face 36 of the piston 32. A wristpin 6t) is mounted inside of the piston 32 to receive the bearing59 in the upper end of the connecting rod. The axis of the wrist pin is preferably disposed between the upper end of the piston 32 and the piston rings 42.

Although the wrist pin 60 may be mounted on the piston 32 in any suitable manner, it should be noted that the conventional open ended, hollow wrist pin driven through the sides of the piston is not suitable because the piston rings cannot be relied upon to seal the pin from the gaspressures developed in the combustion chamber. In order to support the pin 60, a web 61 may be provided inside of the dome 46. The web 61 is adapted to fit into grooves 62 provided on the opposite ends of the wrist pin 60. The wrist pin 60 may be secured to this web 61 by any suitable means such as the screws 62 and nuts 63. In ordertoallow for differences in the amount of-thermal expansion and contraction between the web 61 and pin 69, the screws 62. may have a square shank 64 that fits inside of the rectangular opening 65 in the web 61. The lower edge of the web 61 may be notched at 68 to provide clearance for the enlarged upper end of the connecting rod when it is secured'to thewrist pin 60.

Since the piston 32 is freeto pivot about-the axis of the pin 60, the axis of the piston 32 may become mis aligned with respect to the axis of the cylinder. Movement of the piston 32 into and out ofalignment will produce so-called piston slap which produces undesirable noises and undue wear on the cylinder walls 33; To prevent piston slap, the outside diameter of the skirt 34 normal to the axis ofthe pin 60 issubstantially identical to the diameter of the cylinder. Thus the skirt 34 will slidably engage the walls 38 of the cylinder and reduce the tendency to slap. Since the bearing 59 in the upper end of the connecting rod is a snug fit on the wrist pin tl, there will be no relative movement between the rod and the piston 32 about an axis normal to the axis of the pin 60. Therefore even though there is a limited clearance between the cylinder walls 38 and the piston skirt 34 on a diameter parallel to the pin 60, there will be no piston slap in this. direction. If this diameter is.

made slightly under size as the piston 32 becomes hot during use, the thermal expansion of the web 61 will force the. piston 32, into around shape sothat the skirt; 34 will then engagethe cylinder=walls 38. As the piston- 32 becomes heatedtheweb 61 will expand. This-will stretch the piston so as to. increase the minor diameterand decrease the major diameter. If the proportions are properly chosen, the. decrease in themajor diameter willequal. theincrease dueto. expansion of the piston and the fully expandedweb 61 will make the minor-diameterequal. the major diameter. It should be noted that the face 36- may be made. elliptical similar to theskirt 34' ly decreased. Thus. there will be no piston slap whetherthe piston is hot or cold and yet, there will be room for thermal expansion as .thepiston 32 warms up.

In order to close the=upper end'of the cylinder and thus form a-combustionchamber 44, ahead 70 may be provided for each bank of cylinders 12 and 14. The heads 70 which are. adapted. to be secured to the planar faces 20and 22 on the. block 16 havecavities 72 formed therein to register with-the. openings 18 formed by the cylinders. The walls 74 of this cavity 72 cooperate with the surface of the. face 36 on the piston 32 to define the shape of thecombustion chamber 44.

In order to provide asymmetrical combustion chamber suchas previously described, the surface 74 of this cavity 72. is preferably. a concave surface of revolution developed about theaxisof the cylinder; Althoughany surface may be used, asubstantially hemispherical cavity is shown. The domedface 36 on the piston 32 is provided with a. convex surface 76 of revolution which is face.80 and the center of the cavity 72 cooperate to form a compact volume of revolution that makes up the firing zone 82. Thefiring zone is preferably symmetrical about the axis ofrevolution and contains the majority of the volumeof the combustion chamber 44.

A spark plug 84-may be mounted in the head 70-so that the electrodes 86 thereof project into the firing zone 82 substantially on the axis of revolution. The depressed center. 80 is preferably positionedso that the advancing,- fiame front will strike the center of the surface 80 first and rapidly progress outwardly toward the rim 88 ofthe firing zone 82; Since the distance from the electrodes 86 to the rim 88 is substantially uniform in all directions, the flame front will-reach all parts of the rim 88 simultaneously. Such a compact firing zone 82 will allow a very rapid initial burning of the major portion of the combustible charge without the detonation of any pockets of unburned gases trapped in the firing zone 82.

The peripheral portion 78 of the dome 86 is a portion of a convex spherical surface that closely approaches the periphery of the hemispherical cavity 72 when the piston 32 is at top dead center. These two closely spaced surfaces form an annular quench zone 90symmetrically disposed about the firing zone 82' and having a large surfaceto-volume ratio. When the flame front reaches the rim 88 of the firing zone 82, it will travel into the quench zone 3i) and proceed to burn outwardly through the end gases to the perimeter thereof. Since the quench zone 90 has a very large surface-to-volume ratio, even though the end gases are highly compressed, their temperatures will be maintained below the kindling point so as to prevent detonation. By employing an annular quench zone 98 with the flame front traveling radially a uniform distance in all directions, the maximum amount ofend gases may be burned in the minimum amount of time. This allowsfull advantage to be taken of the quench zone.

By employing an entirely symmetrical. combustion chamber 44 the forces produced on the face 36 of the piston 32 will be balanced. Thus the tendency to cause misalignment of the piston 32 and other troubles present in unbalanced piston assemblies will be greatly reduced or entirely eliminated.

It should be pointed out that as the piston 32 travels upwardly through the cylinder, the gases trapped in the quench zone 90 will be compressed faster than the gases in the firing zone 82, particularly when the piston 32 approaches top dead center. This will result in the quench zone acting as a squish zone 92 that will force the gases to flow radially inwardly along the walls of the combustion chamber 44 towards the electrodes 86 of the spark plug 84. The flow of gases along these walls will produce a scouring action which will tend to remove carbon and other deposits from the valves 94 and 96, walls 74 and electrodes 86. In addition, this violent flow of gases will produce a turbulent action which will thoroughly mix the liquid fuel particles and air in the combustible FhaIrge. This will insure a more complete burning of the Although the intake 94 and exhaust valves 96 may be positioned in any portion of the combustion chamber 44, it has been found to be advantageous to position the valve seats 98 and 100 symmetrically about the axis of revolution. In order to allow more efficient manifolding, it is also desirable to place the exhaust valve seat 100 on the outboard side and the intake valve seat 98 on the inboard side of the heads 70. The intake and exhaust valves 94 and 96 fit in their respective seats 98 and 100 with their stems 102 and 103 projecting outwardly into the valve guides 104 for sliding movement therein. The push rods 106 and 107 and rocker arms 108 and 109 are actuated by a camshaft 110 which is driven by the crankshaft 24 to insure opening of the valves 94 and 96 at the correct time. Coil springs 112 are disposed about the valve stems 102 to oppose the push rods 106 and bias the valves into the closed position. Although the push rods 107 are shown as being horizontally disposed between the diameters of the cylinders, it should be understood that the length of the engine may be decreased by moving the push rods 107 so that they extend above the diameters of the cylinders. This may be accomplished by raising the camshaft 110 or by incining the push rods 107 so that the outer end of the rods will be above the cylinders. This will necessitate inclining the rocker arms 109.

An exhaust port 114 is provided in the side of the head 70 adjacent each exhaust valve seat 100 and is connected thereto by a short straight exhaust passage 116 that discharges directly into the exhaust manifold 118. It is desirable that the length of this passage 116 be as short as possible to reduce the amount of heat transferred from the hot exhaust gases to the head 70. If the valve stem 103 is placed at an angle to the exhaust passage 116, the passage may be straight between the valve seat 100 and part 114.

The intake manifold 120 is a flat or planar type. That is, the corresponding parts of each distribution passage are preferably disposed at the same general elevation and no distribution passage crosses another distribution passage. It should be understood that although the present manifold is substantially a plane, the manifold may be shaped similar to a cylinder or some other suitableform to accommodate its fitting onto the engine or for any other reason. If desired, the heads 70 may be made integral with the manifold 120 in the form of inclined edge portions. The center of the manifold may be provided with a flange 122 for supporting a suitable charge forming device such as a four barrel carburetor 124. The flange 122 may be provided with one or more openings 126 that communicate with a distribution chamber 128 formed in the manifold immediately below the flange 122. The interior of the distribution chamber 128 is interconnected to the centers of the branch passages 130, 132, 134 and 136 by means of distribution passages 138, 140, 142 and 144 that extend outwardly from the chamber 128. The branch passages 130, 132, 134 and 136 extend longitudinally of the manifold 120 so that the opposite ends thereof communicate with the intake valves 94 of adjacent cylinders. The distribution passages 138, 140, 142 and 144 may extend outwardly from the distribution chamber 128 in any suitable manner, however, in the present instance the distribution passages are disposed side by side so as to extend transversely of the manifold 120 from the opposite sides thereof. It should be noted that the passages 138, 140, 142 and 144 are separated merely by partitions 145 and 147. Since each distribution passage is disposed entirely on its own side of the partition, the passages do not have to be in crisscrossing relationship. This permits the passages 138, 140, 142 and 144 to be disposed in substantially the same plane or general level and thereby eliminates the necessity for a bulky and heavy manifold. Thus the manifold 120 may be a simple light weight casting or fabricated from sheet metal.

In order to insure each cylinder obtaining a substantially indentical charge, the distribution passages 138, 140, 142 and 144 may be substantially identical so that there will be substantially the same amount of resistance for the charges flowing through each passage. The present distribution passages include transverse portions 146, 148, 150, 152 and longitudinal portions 154, 156, 158 and 160 that are preferably disposed at right angles to each other. The transverse portions 146, 148, and 152 are connected to the opposite sides of the chamber 128 and extend across the manifold 120 therefrom. The partitions 145 and 147 that separate the transverse portions extend up to the sides of the chamber 128. Thus there will be an unrestricted passage between all of the distribution passages which will permit the combustible charge to be drawn from any portion of the chamber. Thus the charge for any one cylinder may be drawn from all four barrels of the carburetor. The longitudinal portions 154, 156, 158 and 160 preferably have the inner ends thereof connected at right angles to the outer ends of the transverse portions 146, 148, 150 and 152 and the outer ends thereof connected to the centers of the branch passages 130, 132, 134 and 136. It is apparent that the combustible charge for any cylinder will always travel through a distribution passage and half of a branch passage.

In order to provide the maximum volumetric efficiency, it is desirable that the combustible charges flowing through each distribution passage be spaced at substantially uniform time increments. Thus in a four cycle V-eight engine, the charge in each distribution passage is preferably spaced at 360 intervals. There are numerous means for obtaining a firing order that will produce this distribution of flow in the manifold. It has been found that a planar crankshaft 24 in which all of the pistons in each set of four end cylinders move together. A two throw crankshaft may be employed in which four piston rods will be connected to each throw. This in effect will amount to two crankshafts each of which may be separately balanced by suitable counterweights. A planar four throw crankshaft 24 such as shown in Fig. 5 may also be employed. The crankshaft 24 is rotatably supported by a front main bearing 162, a rear main bearing 164, and three intermediate main bearings 166. The front throw or number one throw 47 may be connected to the pistons in cylinders 1 and 5 by means of connecting rods 51 and 55. The second forward throw or number two throw 48 which is connected to cylinders 2 and 6 by connecting rods 52 and 56 may be disposed in the same plane as the forward throw 47 and on the same side of the axis of the crankshaft 24. The rear throw or number four throw 50 and the throw 4-9 immediately in front thereof or number three throw which are connected to cylinders 4 and 8 and cylinders 3 and 7, respectively, by connecting rods 54, 58, 53. and 57 may be in the same plane as the two. forward throws 47 and 48 but disposed on the opposite sides of the crankshaft. Thus the throws 47 and 48 will be 180 out of phase with the throws 49 and 50. In order to. prevent engine vibrations, it may be desirable to balance. the crankshaft 2 4. The two intermediate throws 43 and 49- will be disposed on the opposite sides of the crankshaft 2,45 so that theywill tend to balance each other. However, the number one throw 47 and the number four throw 50 may he provided with counterweights 167 that will tend to, maintain the crankshaft 24 balanced at all times,

If the cylinders are numbered It through 8 starting at the left front cylinder and proceeding towards the rear and then continuing with the right front and proceeding towards the right rear, a firing order of 1, S, 4, 5, 2, 7, 3, 6 will produce firing impulses equally spaced at 90 for clockwise rotation when viewed from the front of the engine. When such a firing. order is employed the combustible charge for cylinder 1 will be drawn through distribution passflgfi 142 first. 90 later the charge for cylinder 3 will be drawn through distribution passage 140. Following this at equally spaced 90 intervals the charges for cylinders 4 and 5 will be drawn through distribution passages 1454 and 13?, respectively. Thus during one revolution of the engine each distribution passage has conducted one combustible charge to a cylinder. As the next revolution begins, air will be drawn through distribution passage 142 for cylinder 2. It should be noted that this charge passes. through distribution passage 142 360 after the charge for cylinder 1'. Following this the charges for cylinders 7, 3 and 6 will pass through distribution passages 1410, M4 and 138, respectively, at 90 intervals so as to be 360 behind the charges for cylinders 25, 4, and 5 which pass through the same passages. It will thus be apparent that by employing this firing order the charges through the distribution passages 138, 140, 142 and 144 will always be evenly spaced so as, to cause the minimum resistance to the flow of air therethrough.

In order to insure that the engine operates at a satisfactory temperature, cooling means may be provided such as a water jacket 170 in the block 16 and an interconnected water jacket 1172 in the head 70. The water jacket 170 in the block 16 surrounds each cylinder in heat exchanging relationship so as to keep the walls 38 thereof sufficiently cool. The water jacket 172. in the head 70 surrounds each valve seat 9 8 and 10%) so as to insure the valves 94 and 96 remaining cool enough to prevent burning thereof. Also it may be desirable to place a portion of the water jacket 172 about the stern 102 of the exhaust valve 96 to prevent an undue accumulation of heat in the exhaust valve 96. However, since the length ofthe exhaust passage 116 in the head 70 is kept to a minimum, the heat transfer to the head 70 is a negligible amount and accordingly, there is preferably no heat transferred from the exhaust gases to the water jacket 172.

While the foregoing description and figures have been confined to one embodiment, it will be apparent to those skilled in the art that numerous modifications may be made without departing from the spirit thereof. Accordingly, it is to be understood that the foregoing is to be considered as illustrative only and in no way restrictive, reference being had to the appended claims to determine the scope of the invention.

What is claimed is:

1. A piston for reciprocating movement in the cylinder of an engine, said piston having a substantially cylindrical skirt and a closed end shaped to form a wall of a combustion chamber, an annular portion of said skirt being adapted to receive sealing means for sliding engagement with the walls of said cylinder, and connecting means cou- 10 pled to said piston between said sealing means and said closed end, a portion of said skirt on the opposite side of said sealing means from said connecting means forming a bearing surface for sliding engagement with said cylinder of said engine.

2 A piston adapted to be secured to a piston rod for reciprocating movement in the cylinder of an engine, said piston comprising a cylindrical skirt for sliding engagement with the walls of said cylinder, a closed end attached to said cylindrical skirt for forming a wall of a combustion chamber, said skirt including a ring belt having at least one annular groove formed therein for supporting a piston ring in sliding engagement with said walls, means for connecting said rod to said piston, said means being mounted inside of said piston and being axially disposed between said ring belt and said closed end, said skirt also including a bearing surface disposed on the opposite side of said ring belt from said connecting means for sliding engagement with said cylinder of said engine.

3. A piston for movement in the cylinder of a reciprocating engine having a head with a cavity formed therein to register with said cylinder, said piston comprising a cylindrical skirt having at least one annular groove therein to receive a piston ring for wiping engagement with the walls of said cylinder and a dome projecting from one end of said skirt to cooperate with said cavity to form a combustion chamber, the periphery of said dome having a convex surface of revolution substantially coaxial with said skirt, the center of said dome having a concave surface of revolution substantially coaxial with said skirt, a wrist pin disposed inside of said piston for attachment to a connecting rod, said pin being disposed between said dome and said groove.

4. A combustion chamber defined by a pair of walls having cooperating surfaces thereon, one of said walls having a concave surface of revolution, the other of said walls having a portion thereof formed to project inside of said concave surface, said portion having a surface of revolution disposed to cooperate with said first surface, said second surface having a convex. peripheral portion and a depressed center portion, each of said portions being substantially coaxial with said first surface, at least one valve seat formed to open directly into the space between said walls.

5. In a reciprocating engine, a block with a cylindrical opening therethrough, a head with a cavity formed therein, said cavity having a surface of revolution disposed to register with the open end of said cylinder, a piston reciprocably disposed in said cylinder, one end of said piston having a surface of revolution disposed to register with the surface. of said cavity when said piston is positioned at the upper end of said cylinder, the peripheral portions of said surfaces being closer together than the center portions of said surfaces when said piston is in said position, at least one valve seat formed in the surface of said cavity to open directly into the space between said surfaces of revolution.

6. In a reciprocating engine, a block having a cylindrical opening therethrough, a head secured to said block, said head having a cavity with a concave surface of revolution positioned to register with the open endof said cylinder, a piston reciprocably disposed in said cylinder with one end thereof having a convex surface of revolution disposed substantially coaxial with said concave surface, said end having a hollow portion forming a de: pressed surface of revolution in the center of said convex surface substantially coaxial therewith, said depressed surface and the center of said concave surface defining a firing chamber when said piston is at the upper end of said cylinder, said firing chamber comprising a volume of revolution, the remainder of said surfaces defining a quench chamber, said quench chamber comprising an annular volume substantially coaxial with said firing chamher, the surface-to-volume ratio. of said quench chamber being substantially greater-than the corresponding ratio of said firing chamber, and valve seats formed in said concave surface to open directly into the space between 'said surfaces on said head and pistons.

7. In a reciprocating engine a block having a cylindrical opening therethrough, a head secured to said block, said head having a cavity with a concave surface of revolution positioned to register with the open end of said cylinder, a piston reciprocably disposed in said cylinder with one end thereof having a convex surface of revolution disposed substantially coaxial with said concave surface, said piston having a depressed portion in said end forming a depressed surface of revolution in the center of said convex surface substantially coaxial therewith, said depressed surface and the center of said concave surface defining a firing chamber when said piston is at the upper end of said cylinder, said firing chamber comprising a volume of revolution, a spark plug mounted in said head and having the electrodes thereof disposed substantially coaxial with said firing chamber, intake and exhaust valve means in said head disposed to communicate with said chamber, the remainder of said surfaces defining a quench chamber, said quench chamber comprising an annular volume substantially coaxial with said firing chamber, the surface-to-volume ratio of said quench chamber being substantially greater than the corresponding ratio of said firing chamber.

8. In a reciprocating engine, a block having a cylindrical opening therethrough, a head secured to said block and having a cavity formed therein, said cavity having a substantially semi-spherical surface positioned substantially coaxial with said. cylinder and having a radius substantially equal to that of said cylinder, a piston reciprocably disposed in said cylinder, a dome on one end of said piston formed to fit inside of said cavity when said piston is positioned at the upper end of said cylinder, the peripheral portion of said dome having a convex spherical surface disposed coaxial with said cylinder and having a radius substantially equal to that of said piston, the center portion of said dome having a depressed surface substantially coaxial with said cylinder, said depressed surface and the center of said concave surface forming a firing chamber having a volume of revolution coaxial with said cylinder, the spherical surface of said peripheral portion and the remaining portion of said concave surface defining an annular quench chamber coaxial with said cylinder, the surface-to-volume ratio of said firing chamber being substantially smaller than the corresponding ratio of the quench chamber, a spark plug mounted in said head and having the electrodes thereof projecting into said firing chamber substantially coaxial therewith, and inlet and outlet valve means in said head communicating with said chambers at points disposed symmetrically about said spark plug.

9. In a reciprocating engine, a block having a cylindrical opening therethrough, a head secured to said block,

said head having a semi-spherical cavity formed therein substantially coaxial with said cylinder and having a radius substantially equal to the radius of said cylinder, a spark plug mounted in said head and having the electrodes thereof projecting substantially coaxially into said cavity, intake and exhaust valve means positioned in said head to communicate with said cavity substantially symmetrically about said spark plug, a piston reciprocably disposed in said cylinder, a semi-spherical dome projecting coaxially from one end of said piston to fit inside of said cavity when said piston is disposed at the upper end of said cylinder and having a radius substantially equal to that of the piston, said dome having a substantially spherical depression coaxially disposed in the center thereof substantially concentric with said electrodes when said piston is in said position.

10. In an engine having a cylinder block with a cylinder extending therethrough, a head secured to said block, said head having a cavity positioned therein to register with one end of said cylinder to form a combustion chamber, an exhaust port formed in one side of said head adjacent said combustion chamber, an exhaust valve seat formed in said head to communicate with said combustion chamber adjacent said side, and a substantially straight passage formed in said head between said exhaust port and said exhaust valve seat.

11. In an engine having a cylinder block with a cylinder extending therethrough, a head secured to said block, said head having a cavity positioned therein to register with one end of said cylinder to form a combustion chamber, an exhaust valve seat formed in said head adjacent one side thereof to communicate with the side of said combustion chamber closest to said side, an intake valve seat formed in the opposite side of said head so as to communicate with the opposite side of said combustion chamber, an exhaust port formed in said side adjacent said exhaust valve seat, and a substantially straight exhaust passage interconnecting said port and said exhaust valve seat.

12. In a cylinder head having cavities formed therein to register with a bank of aligned cylinders to form combustion chambers, ignition means projecting through said head into the centers of each of said combustion chambers, a plurality of inlet valve seats formed in said head adjacent one side thereof, each of said seats being positioned to communicate with one of said combustion chambers on one side of said ignition means, a plurality of exhaust valve seats formed in said head adjacent the other side thereof, each of said exhaust seats being positioned to communicate with one of said combustion chambers, said inlet and exhaust valve seats being disposed diametrically about said ignition means, an exhaust port formed in said second side of said head adjacent said exhaust valve seat, and a substantially straight exhaust passage disposed between said exhaust seat and said port.

13. A piston adapted for reciprocating movement in a cylinder of an engine comprising a substantially cylindrical skirt portion, a closed end attached to said cylindrical skirt for forming one wall of a combustion chamber, a web in the interior of said piston attached to the inside of said closed end and a portion of the inside of said skirt, a wrist pin in the interior of said piston having an axis generally parallel to said web and being adapted to receive the upper end of a connecting rod, said skirt including bearing surfaces disposed on diametrically oppo site sides and normal to the axis of said wrist pin.

14. A piston adapted to be secured to a piston rod for reciprocating movement in the cylinder of an engine, said piston comprising a cylindrical skirt for sliding engagement with the walls of said cylinder, a closed end attached to said cylinder skirt for forming one wall of a combustion chamber, said skirt including a ring belt having at least one annular groove formed therein for supporting a piston ring in sliding engagement with said walls, a wrist pin inside of said piston between said ring belt and said closed end adapted to be connected to said piston rod, said skirt including bearing surfaces on the diametrically opposite sides thereof normal to the axis of said wrist pin and on the side of said ring belt most remote from said closed end.

15. A piston adapted to be secured to a piston rod for reciprocating movement in the cylinder of an engine, said piston comprising a cylindrical skirt for sliding engagement with the walls of said cylinder, a closed end attached to one end of said cylindrical skirt for forming a wall of a combustion chamber, bearing surfaces formed on diametrically opposite sides of said skirt adjacent the other end thereof for sliding engaging with the walls of said cylinder, a wrist pin disposed inside of said piston between said bearing surfaces and said closed end, a ring belt disposed between said wrist pin and said bearing surfaces for receiving piston rings for sliding engagement with said cylinder walls.

16. A piston adapted to be secured to a piston rod for 13 reciprocating movement in the cylinder of an engine, said piston comprising a cylindrical skirt for sliding engagement with the walls of said cylinder, a closed end attached to one end of said cylindrical skirt for forming a wall of a combustion chamber, bearing surfaces formed on diametrically opposite sides of said skirt adjacent the other end thereof for sliding engagement with the walls of said cylinder, a wrist pin disposed inside of said piston between said bearing surfaces and said closed end, a ring belt disposed between said wrist pin and said bearing surfaces for receiving piston rings for sliding engagement with said cylinder walls, a planar web disposed in the interior of said piston and attached to the inside of said closed end and a portion of said skirt and being substantially parallel to the axis of said wrist pin.

References Cited in the file of this patent UNITED STATES PATENTS 564,577 Altham July 21, 1896 1,012,635 Harmer Dec. 26, 1911 1,414,384 Tartrais May 2, 1922 FOREIGN PATENTS 568,101 Germany Jan. 14, 1933 

